Fiber optic cables can be employed in a variety of applications including the transmission of voice and data in cable television, computer and telephone systems. Fiber optic cables can generally be classified into two categories, namely, trunk and distribution cables that are designed to span relatively long distances, and drop cables that span much shorter distances and that typically terminate at a home or business. Trunk and distribution cables are generally relatively large and rigid. For example, trunk and distribution cables typically include a relatively thick jacket and large core components protecting the optical fibers. Trunk and distribution cables can include one or more strength members resisting sharp twists or turns of the cable. As a result of their construction, trunk and distribution cables are generally expensive.
In contrast to trunk and distribution cables, fiber optic drop cables are typically relatively flexible. This flexibility facilitates twisting and turning of the drop cable during installation. Since fiber optic drop cables generally include fewer optical fibers and extend across shorter distances than fiber optic trunk and distribution cables, fiber optic drop cables are comparatively smaller and less expensive.
The introduction of water into a fiber optic cable and the migration of water therethrough can be a problem. Fiber optic cables typically define one or more internal passageways through which the optical fibers extend. Water that enters the passageway can migrate in the internal passageway and be conducted to a closure or other termination device. The water can then physically degrade the closure or other termination device and/or can damage electronics mounted within the closure or other termination device. In addition, any water that remains in the passageway defined by the fiber optic cable can disadvantageously subject the optical fibers to additional forces if the water were to freeze.
Several methods have been employed to inhibit the migration of water. For example, fiber optic cables have included a hydrophobic grease or gel that fills the internal passageways. While the hydrophobic grease or gel blocks the migration of moisture through the passageways, the fiber optic cable must be designed and the hydrophobic grease or gel must be selected such that the hydrophobic grease or gel is compatible with the materials that form the other elements of the fiber optic cable with which the hydrophobic grease or gel may contact. A buffer tube can define the internal passageway that is filled with hydrophobic grease or gel, in which case the buffer tube may have to be formed of a more expensive compatible polymer. In addition, fiber optic cables that include a hydrophobic grease or gel are generally more difficult to handle during their manufacture, installation and repair.
Fiber optic cables have also been designed that include elements formed of water swellable material, for a super absorbent polymer. The water swellable material is typically carried by yarns or tapes that are disposed within a passageway in the fiber optic cable. Upon contact with water, the water swellable material will absorb the water and swell so as to physically close the passageway, thereby preventing migration of water through the passageway. See, for example, U.S. Pat. Nos. 5,684,904 and 5,039,197, the contents of both of which are expressly incorporated herein by reference.
While various fiber optic cables have been designed to prevent the introduction of water into and the migration of water through the internal passageways defined by the fiber optic cables, most of these fiber optic cables are relatively large and/or expensive cables that are best suited for use as trunk and distribution cables.